In recent years, demand for portable electronic products such as notebook computers, video cameras, portable telephones and the like has been drastically increased and electric vehicles, storage batteries for energy storage, robots, satellites and the like have been actively developed. For this reason, high performance secondary batteries capable of repeated charge and discharge have been actively studied.
Lithium secondary batteries currently commercially available include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries and lithium secondary batteries. Among them, the lithium secondary batteries are in the spotlight because they have almost no memory effect compared to nickel-based secondary batteries, and thus perform charge and discharge freely, have very low self-discharge rate and have high energy density.
A battery module generally has a basic structure including a plurality of unit cells connected in series or in parallel. Recently, as a need for a large-capacity structure has increased along with the increased use as an energy storage source, a battery system having a structure in which a plurality of battery modules are connected in series or in parallel has been widely used. For example, the battery system may be loaded in an energy storage system for storing and transporting a large amount of power.
The battery system may be implemented in various forms. In order to improve the efficiency in control, the battery system may be configured to be combined with a plurality of BMSs which take charge of controlling a plurality of battery modules included therein, respectively.
The existing battery system may further include a plurality of battery management systems (BMSs) for monitoring and controlling a state of a unit cell by applying an algorithm for controlling power supply to a driving load (e.g., a motor) of a battery module included therein, measuring a characteristic value such as a temperature, a current and a voltage at charging and discharging, controlling equalization of a voltage, estimating a state of charge (SOC) and the like.
If the battery system is loaded in an energy storage system or the like, the temperature of the battery modules included therein may frequently out of a proper range due to its operation (for example, charging or discharging) or external environments, which may shorten the life of the battery system or deteriorate the overall performance of the battery system. To solve this problem, a technique of cooling a battery module using a cooling fan has been disclosed. However, in this technique, it is possible to lower the temperature of the battery module, but it is impossible to lower a temperature deviation among a plurality of battery modules.